[094/nnn] poly_int: expand_ifn_atomic_compare_exchange_into_call

[Richard Sandiford <richard.sandiford@linaro.org>]

This patch makes the mode size assumptions in
expand_ifn_atomic_compare_exchange_into_call a bit more
explicit, so that a later patch can add a to_constant () call.


2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* builtins.c (expand_ifn_atomic_compare_exchange_into_call): Assert
	that the mode size is in the set {1, 2, 4, 8, 16}.

Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c	2017-10-23 17:22:18.226824652 +0100
+++ gcc/builtins.c	2017-10-23 17:25:41.647742640 +0100
@@ -5838,9 +5838,12 @@ expand_ifn_atomic_compare_exchange_into_
   /* Skip the boolean weak parameter.  */
   for (z = 4; z < 6; z++)
     vec->quick_push (gimple_call_arg (call, z));
+  /* At present we only have BUILT_IN_ATOMIC_COMPARE_EXCHANGE_{1,2,4,8,16}.  */
+  unsigned int bytes_log2 = exact_log2 (GET_MODE_SIZE (mode));
+  gcc_assert (bytes_log2 < 5);
   built_in_function fncode
     = (built_in_function) ((int) BUILT_IN_ATOMIC_COMPARE_EXCHANGE_1
-			   + exact_log2 (GET_MODE_SIZE (mode)));
+			   + bytes_log2);
   tree fndecl = builtin_decl_explicit (fncode);
   tree fn = build1 (ADDR_EXPR, build_pointer_type (TREE_TYPE (fndecl)),
 		    fndecl);